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1.
Revealing the evolution of the past geomagnetic field is of dual interest. It is crucial to estimate the conditions of the Earth's deep interiors, while it offers a reliable absolute dating tool of burned archaeological artifacts. Although a substantial effort was paid during the last decade to construct a reference archaeomagnetic curve for Mesoamerica, mostly absolute intensity variations are revealed for the previous three millennia. Here, we report an updated directional (inclination and declination) reference secular variation curve based on volcanic lava flows and archaeological artifacts carrying full thermoremanent magnetization. A bootstrap method with penalized cubic b-splines was used to develop the directional curve. Relocation error exercise and strict selection criteria allowed to use 82 well-defined palaeodirections. Both data distribution density and the firm relationship between the ages and samples, ensure the reliability of the curve for the dating purposes. The combination of directional data with available intensity variation highlights some sudden geomagnetic field fluctuations.  相似文献   

2.
This paper examines the limitations and deficiencies of the current British archaeomagnetic calibration curve and applies several mathematical approaches in an attempt to produce an improved secular variation curve for the UK for use in archaeomagnetic dating. The dataset compiled is the most complete available in the UK, incorporating published results, PhD theses and unpublished laboratory reports. It comprises 620 archaeomagnetic (directional) data and 238 direct observations of the geomagnetic field, and includes all relevant information available about the site, the archaeomagnetic direction and the archaeological age. A thorough examination of the data was performed to assess their quality and reliability. Various techniques were employed in order to use the data to construct a secular variation (SV) record: moving window with averaging and median, as well as Bayesian statistical modelling. The SV reference curve obtained for the past 4000 years is very similar to that from France, most differences occurring during the early medieval period (or Dark Ages). Two examples of dating of archaeological structures, medieval and pre-Roman, are presented based on the new SV curve for the UK and the implications for archaeomagnetic dating are discussed.  相似文献   

3.
A numerical simulation of the 26th December, 2004 Indian Ocean tsunami of the Tamil Nadu coastal zone is presented. The simulation approach is based on a fully nonlinear Boussinesq tsunami propagation model and included an accurate computational domain and a robust coseismic source. The simulation is first confronted to available tide gauge and runup observations. The agreement between observations and the predicted wave heights allowed a reasonable validation of the simulation. As a result, a full picture of the tsunami impact is provided over the entire coastal zone Tamil Nadu. The processes responsible for coastal vulnerability are discussed.  相似文献   

4.
We present an updated compilation of Greek directional archaeomagnetic data for the last 4.5 millennia. The data set comprises 89 directions from archaeological artefacts and volcanic rocks. Most of the data come from the Late Bronze Age (1700-1400 BC) that is the flourishing period of the Minoan civilization in Crete, while parts of the classical (480-323 BC), Hellenistic (323-31 BC) and Roman (146 BC-330 AD) periods are also well covered. The dataset has been analysed using the Bayesian approach for curve building and a directional secular variation (SV) curve for Greece is proposed. Comparisons with regional and global model predictions show a general agreement even though some discrepancies are observed for some time intervals. The new curves together with the previously published intensity SV curve for Greece, also using the Bayesian approach, form a homogeneous set and enrich our knowledge of the full geomagnetic field vector variation in Greece during the last millennia.  相似文献   

5.
A sequence of 25 bread-kiln floors was sampled for archaeomagnetic measurements in a bakehouse in the old town of Lübeck, Germany. Due to archaeological dating this kiln floor sequence has been built up presumably from the late 13 th to the 18 th century. The primary magnetisation component is carried by magnetite (maghemite) and is very stable. Small viscous magnetisation components could be removed easily. The preliminary results of characteristic remanent magnetisation for 23 of the kiln-floor layers show clearly the trend of the geomagnetic secular variation expected for that time interval. By comparison with French and British master curves, the kiln-floor sequence started around 1425 and lasted until 1775 AD. Presently, confidence circles are relatively large and need refineing by measuring more samples, which have already been collected. Together with 14 C dating that can be determined from the charcoals found in the lowest layers and thermoluminescence dating of the layers, we expect to obtain, for the first time, a secular variation curve for Northern Germany covering the time interval from 1400 to 1800 years AD.  相似文献   

6.
New paleomagnetic determinations satisfying the up-to-date methodical and instrumental standards of paleomagnetic studies are obtained from the lava flows and volcanic ash of the Northern Group of Kamchatka volcanoes. In the past 4000 years, 12 stratigraphic levels with tephrostratigraphic ages are explored. The obtained directions of the geomagnetic field fill a gap in the data on the secular variation for northeastern Asia and can be used for developing global models. Besides, a promising outlook for the use of the variations of the geomagnetic field for the regional correlation of volcanic events is demonstrated.  相似文献   

7.
Results from joint work between the Geophysical Institute (Sofia, Bulgaria), and the Geomagnetic Institute (Grocka, Yugoslavia) on the geomagnetic field variation in the prehistoric past are presented. Preliminary curves of variation of the three geomagnetic elements: declination, inclination and intensity are presented. The movement of the virtual pole position for the 6500 years time period B.C. is derived. The curves and the virtual pole positions provide a dating tool for archaeological purposes and determination of the periodicities in the geomagnetic secular variations in southeastern Europe.  相似文献   

8.
Directional secular variation of the geomagnetic field over the last 2000 years has been defined in western Europe from numerous archeomagnetic studies. However, the number of archeomagnetic results for older periods is much more limited. For this reason, we present new data obtained from fired archeological structures found in two French sites (Loupiac and Aspiran) dated within the first millennium b.c. (latest Bronze-earliest Iron Age transition, ∼850-700 b.c. and Iron Age, ∼525-475 b.c., respectively). From a compilation of archeomagnetic results from western Europe (Great Britain, Italy and France) and northern Africa (Tunisia), we propose a directional secular variation curve for western Europe that covers the entire first millennium b.c. This curve exhibits a large clockwise motion with rapid changes during the first half of the millennium, while the last four centuries b.c. are characterized by weak variations.  相似文献   

9.
A detailed study of the ancient intensity of the Earth's magnetic field in Tamilnadu, India is presented using pottery, bricks, tiles etc., obtained from the excavations that have been carried out at some of the important places of historical and archaeological interest. An attempt is made to reconstruct the secular variation of the geomagnetic field intensity. The results reported here reveal considerable changes in the Earth's magnetic field in this region during the past 2400 y. It is observed that the intensity of the geomagnetic field has been previously 57% greater than at present.  相似文献   

10.
Abstract

A monthly rainfall-runoff model was calibrated for a large tropical catchment in southern India. Various land-use and climatic change scenarios were tested to assess their effects on mean annual runoff and assured water yield at the Bhavanisagar Reservoir in Tamil Nadu, India. The largest increase in runoff (19%) came from converting forest and savanna (the indigenous control scenario) to agriculture. Mean annual runoff decreased by 35% after conversion to commercial forest and 6% after partial conversion to tea plantations. The predicted climate scenarios of reduced dry season rainfall decreased the annual runoff by 5% while enhanced annual rainfall caused a 17% increase in runoff. Even if land-use and climate changes had relatively large effects on runoff, the changes in reservoir yield which can be assured every year, were often less severe. This was probably due to the buffering effect of the reservoir and variation in the mean annual runoff.  相似文献   

11.
Archaeomagnetism in Greece has continuously developed during the last decades. Numerous studies have provided high quality data and accurate secular variation curves for the direction and intensity of the geomagnetic field have been constructed. The Greek Secular Variation Curves (SVCs) cover the last 8 millennia for intensity and 6 millennia for direction. The coverage of the archaeological periods remains uneven, with several gaps, mostly in the directional dataset, with only two results for periods older than 2500 B.C. In the present contribution, the first archaeomagnetic results from Neolithic settlements in northern Greece are presented. For the present study, samples were collected from three different archaeological sites: burnt structures in Avgi (Kastoria) and Vasili (Farsala) and one oven from Sosandra (Aridaia). The natural remanent magnetization (NRM) grouping of all specimens indicated that the majority of the samples were burnt in situ, providing thus a reliable direction of the ancient field. Magnetic cleaning (both alternating-field and thermal) revealed the presence of one stable component of magnetisation. Rock magnetic experiments (acquisition of isothermal remanent magnetization (IRM), thermal demagnetisation of the IRM, thermomagnetic curves) have been performed on pilot samples indicating that low coercivity magnetic minerals such as magnetite or Timagnetite are prevailing. The mean directions (declination D, inclination I and parameters of the Fisherian statistics), which arose from the three sites are as follows: Sosandra: D = 343°, I = 55.6°, ??95 = 4.8°; Avgi: D = 10.1°, I = 53.4°, ??95 = 4.2° and Vasili: D = 357.5°, I = 43.1°, ??95 = 4.1°. The obtained data are in a very good agreement with results from Neolithic Bulgaria. This study represents the beginning of an effort to fill the gaps of the Greek secular variation curves and their extension to the Neolithic period.  相似文献   

12.
Stable isotope measurements in precipitation help us to form the basic inference about the origin and the state of water in different environments. The precipitation samples collected during the South West Monsoon (SWM) during August 2007 from 37 different locations in the state help in deriving the first preliminary local meteoric water line (LMWL) for the Tamil Nadu State. The study reveals that there are three main sources of water vapours, namely South East Arabian Sea (SEAS), Indian Ocean (IO) and evaporation from local water bodies. There are wide variations in the altitude and amount of rainfall received in the state. It is also noted that there is a significant variation in the latitude and the distance from the coast. Hence, an attempt is made in this paper to study the factors controlling the composition of stable isotopes in precipitation with reference to amount of rainfall, latitude, altitude and the continental effect. The altitude and continental effect shows good correlation to the variations in stable isotope composition. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

13.
Discovered accidently during factory building construction works, the Middle Palaeolithic site of Biache-Saint-Vaast (Pas-de-Calais, France) was excavated from 1976 to 1982 by a team of Lille University directed by Alain Tuffreau. An abundant archaeological and paleontological material, including two human skulls, was there recovered from fossil alluvial deposits of the Scarpe River. In order to determine the ages of these remains, the ESR/U-series method was applied on bone and teeth. As the U-series data obtained of the main part of the analyzed tissues do not allow the use of the classical US-ESR model, the recently proposed AU-ESR model, taking into account if necessary U-leaching from some of the tissues, was used to calculate combined ESR/U-series ages for these samples. The obtained ages suggest a MIS7 attribution to the faunal remains and permit an age of ca 240 ka to be assigned for the human remains and associated archaeological material, in accordance with the stratigraphic data and the large mammal associations.  相似文献   

14.
It is critical that a comprehensive terrestrial radiocarbon (14C) calibration curve is developed beyond 26 ka for high-precision calibration and correlation of climatic, environmental and archaeological records. Abundant sub-fossil New Zealand kauri (Agathis australis) wood, preserved in Oxygen Isotope Stage-2 and 3 peat swamps, provides an important resource for 14C calibration; nowhere else in the world does such an extensive collection of ancient wood exist. Although finite 14C ages beyond 50 ka are becoming routinely reported, few attempts have been made to demonstrate their accuracy or precision. Finite ages beyond 50 ka require optimization of all elements involved in sample preparation and 14C analysis. Here we discuss the methodology employed for optimizing the 14C dating of near-background wood samples by both benzene synthesis for liquid scintillation counting (LSC) or graphite synthesis for accelerator mass spectrometry (AMS). We report the mean background blank activities for both methods and present a statistical model for assigning blank standard errors when blank activity variation is over and above counting statistics. We also present duplicate analyses (using LSC and AMS) of nine successive samples of wood obtained from a sub-fossil kauri log near-background in age to investigate the significance of the measured blank levels and variability.  相似文献   

15.
李献华 《地球物理学报》1998,41(Z1):184-194
综合了前人和作者最新的地质年代学和地球化学研究成果,对华南晚元古代晋宁期造山运动的演化提供了化学地球动力学制约晚元古代早期（0．97－1．0Ga）的皖南、赣东北和桂北蛇绿岩在元素地球化学上具有相似的岛弧特征,但它们的Nd同位素组成明显不同新获得的高精度结石U－Ph年龄资料表明,桂北地区的本洞、三防和元宝山等三个主要花岗岩岩体均形成于820-825Ma,排除了本区有中元古代晚期花岗岩的存在．扬子南缘中元古代到三叠纪各个时代地层中的泥质沉积岩的TDM在晚元古代早期从约1．8Ga急剧降低至约1．3Ga,反映了这个时期的沉积物源区有大量新生馒源物质的加入．根据研究资料,提出了华南和扬子块体晋宁期陆-弧-陆碰撞模式  相似文献   

16.
Direct measurements of the Earth's magnetic field in Italy since 1640 a.d. have been used to check the remanence directions derived from historically dated volcanic rocks of Etna and Vesuvius. Direct measurements consist of the records of L’Aquila and Pola geomagnetic observatories, the repeat stations of the Italian Magnetic Network and the data base of the Historical Italian Geomagnetic Data Catalogue. All have been relocated to the same reference site (Viterbo — lat. 42.45°N, long. 12.03°E) in order to draw a reference secular variation (SV) curve. The direction of the Earth's field at Viterbo has also been calculated from the historical records (2000-1600) of ref. [Jackson, A., Jonkers, A.R.T., Walker, M.R., 2000. Four centuries of geomagnetic secular variation from historical records. Phil. Trans. R. Soc. London, Ser. A 358, 957-990] database. The remanence directions from Etna show a general agreement with the trend of the SV curve, although their inclination is usually lower than that from the direct measurement. The directions from Vesuvius are more scattered. Large discrepancies occur at both volcanoes and in some cases have been ascribed in the literature to poor geographic information, making it difficult to identify the flows actually emplaced during the eruptions reported in the chronicles. Closer examination shows that the great majority of the best-defined remanence directions (semi-angle of confidence α95 < 2.5°) deviate significantly from the geomagnetic direction measured at the time of the emplacement, the angle between the two directions being larger than the α95 value. The value of 2.5-3.0° can thus be regarded as a conservative evaluation of the error when dealing with dating Etna and Vesuvius lava flows older than 17th century, even when the accuracy attained in remanence measurements is higher. In default of a SV curve for Italy derived from archaeological artefacts, a further error in dating is introduced when reference is made to SV curves of other countries, even if well-established, as these are from regions too far from Italy (>600 km) to confidently relocate magnetic directions.  相似文献   

17.
第11代国际地磁参考场(IGRF-11)是国际地磁学与高空物理学联合会(IAGA)于2009年12月提出的最新与比较准确的IGRF.根据IGRF-11模型,计算了2005-2010年中国地区地磁长期变化(SVC).IGRF-11所描述的2005-2010年中国地区地磁长期变化与实际观测的地磁长期变化(SVO)是基本一致的,但亦有明显差异.分析比较了在中国地区34个台站上的SVO与SVC之间的差异,并得到了它们之间的差值及其均方误差σ,对于地磁偏角和倾角,σ分别为0.35′/a与0.53′/a;对于地磁总强度、水平分量、北向分量、东向分量与垂直分量,σ分别为5.12nT/a,8.91nT/a,8.89nT/a,3.27nT/a与3.59nT/a.引起IGRF-11所描述的2005-2010年中国地区地磁长期变化的误差原因是:中国地区的区域性与局部性的磁异常、IGRF忽略了外源场与IGRF模型的截断阶数、全球台站与测点的分布不均匀、地磁观测误差等因素.由于中国地磁模型(CGM)优于IGRF模型,并能比较准确地描述中国地区地磁场及其长期变化,故在实际应用中应选用CGM.  相似文献   

18.
—The study presents the results of the statistical relationship between seasonal northeast monsoon rainfall over Tamil Nadu state of India (TNR) and southeast India (SER) and mid-latitude circulation indices viz., zonal index (ZON) meridional index (MER) and the ratio of meridional to zonal index (M/Z) between the geographical area 35°N to 70°N at 500 hPa level over three sectors and hemisphere, based on 19 years (1971–1989) of data. The results indicate that northeast monsoon rainfall over India shows a strong antecedent relationship with the strength of ZON over all the sectors and hemisphere. The best association is observed during antecedent March over sector I (45°W–90°E) where direct and strong correlation coefficients of 0.69 and 0.64 are obtained with TNR and SER, respectively. Antecedent MAM (spring) season over sector I also shows a significant positive correlation with TNR/SER. Thus, the mid-latitude zonal circulation index may have possible use for the long-range forecasting of northeast monsoon rainfall over India.  相似文献   

19.
The spatial-temporal model of the geomagnetic field has been constructed using the data of the high-accuracy survey of the CHAMP German satellite, obtained during its operation from May 2001 to September 2007. The daily average spherical harmonic models calculated at an interval of four days are used as initial data in order to expand these models by the method of natural orthogonal components (NOCs). It has been indicated that the obtained NOC series rapidly converges. The secular variations, secular acceleration, and Dst variation are distinguished as individual NOC components, which makes it possible to construct the spatial-temporal field model. In addition, the models-predictions have been constructed for the year 2008 based on the candidate models of the main field and the secular variation for the year 2005, which were used to obtain the IGRF2005 international model. A comparison of the models-predictions with the model constructed for the year 2008 using our method indicated that the accuracy of our model is not lower than that of the models, obtained by other scientific groups using the traditional method.  相似文献   

20.
A secular variation record of the geomagnetic declination has been obtained from glaciolacustrine varved clays and postglacial sediments, sampled both from outcrop and from piston cores from Lake Ontario. It appears to be uninterrupted and covers the interval 14,000 years B.P. (14C) to the present. The record for the interval 14,000–12,300 years B.P. consists of true declination and was obtained from samples collected from outcrop. The record for the interval 12,500 + years B.P. to the present consists of relative declination and was obtained from piston cores. The secular variation record is internally consistent and is compatible with the chronology of events known to have occurred during and following the deglaciation of western New York. Use of the record for magnetic correlation within the study area is demonstrated.  相似文献   

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